Production of metal powders from their oxides



March l2, 1957 C, F, TElcHMANN 2,785,061

PRODUCTION OF METAL POWDERS FROM THEIR OXIDES Original Filed Sept. 13.1952 2,785,061 Patented Mar. 12, 1957 PRODUCTION GF NIETAL PWDERS FROMTHER GXDES Charles E'. Teichmann, Crestwood, N. Y., assigner to TexacoDevelopment Corporation, New York, N. Y., a corporation of BelawareOriginal application September 13 1952 Serial No. strasse. niviaee andthis appnftion time 2s, 1956, Serial No. 593,338

10 Claims. (Cl. 75-.5)

This invention relates 4to a novel method for preparing metals fromtheir oxides. By this method metal powders can be prepared continuously,rapidly, and economically with average particle sizes smaller than 40microns and even as small as 1 5 microns or less. It is also possible toprepare liquid metals more rapidly and efliciently than heretofore.Among the metals which can be prepared by my process are those belowchromium in the electrochemical series.

In accordance with the principles of the present invention there isprovided a novel method for producing a comminuted metal from a readilyreducible metal oxide which comprises forming a slurry of particles ofthe metal oxide in a vaporizable liquid, such as water or kerosene or anoil-water emulsion, for example, and passing the slurry into a heatingzone wherein it is heated -to a temperature surhcient to evaporatesubstantially all of the liquid. Particles oi metal oxide then arecarried by the resulting vapor at high velocity in violently turbulentow through a long tube to disintegrate any solid particles and decreasetheir size.

Reduction or" the oxide to the metal is accomplished by reacting theoxide with a reducing gas such as hydrogen, carbon monoxide, or ahydrocarbon such as methane. The reactions are almost stoichiometric,less than l() percent excess reducing gas generally suf'ricing. Thereducing gas may be introduced into the long tube to react with themetal oxide while maintaining the high velocity turbulent flowconditions to etiect disintegration of particles flowing with the vapor,and while maintaining the temperature below the melting point of themetal, to produce as a product comminuted metal much liner than theparticles of metal oxide initially passed into the heating zone.Alternatively, the nely divided metal oxide powder may be separated fromthe vapor and then reduced in a separate reactor. Liquid metal isobtained when the temperature in the reduction zone is above the meltingpoint.

The invention will be described in detail below with eference to theaccompanying drawings wherein:

Fig. l is a schematic View of one type of apparatus suitable forperforming my novel method by both grinding and reducing the metal oxidein the same long tube; and

Fig. 2 is a schematic view of apparatus suitable for performing amodified embodiment of my novel method by grinding the metal oxide in along tube, and then reducing it in a separate reactor.

In performing my novel method particles of metal oxide are introducedinto a mixer 11 wherein they are mixed intimately with a vaporizableliquid such as water or kerosene to form a purnpable slurry. The metaloxide particles should be small enough to oe handled readily as asuspension or slurry, particles as large as 5 mm. diam eter down to.07Ar mm. or 'less being satisfactory. Enough liquid should be added toproduce a slurry which consists at least 35 percent of liquid by weight.In some instances it may be desirable to mix an inert solid materialsuch as bentonite with the slurry, and a solid reducing material such ascarbon can also be added, with or without theinert.

The slurry is transferred by a pump 13, such as a piston type mud pump,through a preheater 15 and into an elongated coiled tube 17 containedwithin a heater 19, such as a fuel-tired furnace. A tube 17 having aninside diameter of 1/a inch and a length of 150 to 1,000 feet can beused. it need not necessarily be coiled for operability ot' the method,but a coil is advantageous for compactness and heating eiiiciency.

The initial section of the tube 17 constitutes the heating zone in whichthe liquid is heated up to its boiling point and the particles of metaloxide are also concurrently heated. Part-way through the tube 17 theboiling temperature is reached and the liquid is converted to a largevolume of vapor which ows at a high velocity in an extremely turbulentmanner through the tube, carrying particles of disintegrating metaloxide with it. The vapor and metal oxide particles then pass out or"tube 17 into a similar coiled long reaction tube 18 having severalspaced inlets for reducing gas connected to a supply conduit 21.

The reducing gas immediately starts to react with the particles of metaloxide flowing turbulently at high velocity with the vapor in tube 1S andconverts them to metal as they pass through the tube to its outlet 23.Further reduction in particle size occurs in tube 18.

The reducing reaction is sniciently exotherrnic with most metal oxidesthat external heating of the reaction tube 18 usually is unnecessary tomaintain high velocity vapor ow. In fact, so much heat energy generallywill be liberated that tube 18 should be cooled, as by water jets from asprayer 2d, when an economically high production rate is employed.Cooling can be dispensed with when a sufficiently small throughput ofmetal oxide is employed, and when the reducing fluid is suicientlydilute, but a lower production rate is then obtained.

Tubes 17 and 18 actually constitute two parts of a single Ilong tubewherein grinding and reducing occur. It is apparent `that both 17 and 18could be composed of two or more parts, each lying within its ownheating furnace or cooling vessel, or they could both be located withinthe same enclosure.

The extremely high velocity turbulent ilow maintained within the tubes17 and 1S causes the particles of metal oxide, before reduction, and theparticles of metal, after reduction, to impinge against one another anddisintegrate to powder of greatly decreased size compared to theparticles of oxide originally in the slurry.

The vapor and metal powder are discharged from the tube 1S throughoutlet 23 and ow to a separator 25 such as a conventional cycloneseparator wherein the vapor and metal particles are separated from oneanother, the metal dropping out of suspension and being discharged as asubstantially dry powder through the outlet 27, and the vapor (includingany excess reducing gas and gaseous products of the reaction) leaving atthe top through an outlet 29. Y

For economy the separated hot vapor is passed by a conduit 3l to slurrypreheater 15. Any uncondensed vapor then passes to a scrubber 32 whereinall-but the excess reducing gas is removed,.after which the excessreducing gas passes by a conduit 33 into the supply conduit 21.

The type `of scrubber 32 depends upon the type `of reducing gas employedin the operation. When the reducing gas is hydrogen, it -is onlynecessary to condense ywater vapor. When the reducing fluid is carbonmonoxide it is only necessary to absorb carbon dioxide in a Acausticsolution, or the like. When the reducing duid is a hydrocarbon, such asmethane, provision must be made -both for condensing Water vapor and forabsorbing carbon dioxide.

Further economy can be realized byV recycling con# densed water to lthemixer 1-1, if desired. Any nelyrdivided metal carried over with theseparated vapor can be filtered or scrubbed out if such recovery iseconomically justified. Any unconvertcd metal oxide leaving theseparator 25 can be segregated and recycled tothe mixer 11. y

In carrying out the method described above it is advantageous for theslurry entering the tube 17 to have a linear velocity at least between1/2 and 10 feet per second, suitably about lrfoot per second. Efiicientgrinding of solid material in the tubes 17 and 18 is obtained w-hen thevapor velocity therein is between 100 and 3,000 feet per second, withvelocities above 200 -feet per second being especially desirable. Highervelocities may be used,

and pressures up to 500 pounds per square inch gauge or higher can beused.

The reduction temperatures vary for the different metal oxides, typicalexamples being set forth below. With copper oxide the reaction wit-hhydrogen will proceed at temperatures above about 140 C.; with carbonmonoxide, 4above about 130 C.; with methane, above about 530 C. Hydrogenalso starts to reduce Zinc oxide at `about 310 C.; lead monoxide atabout 185 C.; and cadmium oxide at about 280 C. Iron oxide can beyreduced by hydrogen at SOO-600 C.; nickel oxide at about 300 C.; cobaltoxide at 500-600 C. (reduction starting at about 165 C.); tin oxide at70D-800 C.; maganese monoxide at about 1,200 C.; but at a considerablylower `temperature at high pressures, e. g., 200 C. at 150 atm. Cobaltoxide can be reduced with carbon monoxide at about 600 C. Lead monoxidecan be reduced with methane at about 750 C. The reaction temperatureactually employed should in every case be high enough to assure theproduction of suiieient steam or other Vapor for grinding. The toptemperature should be 'below the melting point of the metal when metalpowder is wanted, since molten metal would be produced above `themelting point.

Using the production of finely-divided copper metal from copper oxideparticles as an example, the principles of the invention may lbe appliedby rst making up a water slurry consisting about 50 percent by weight ofcopper oxide particles Vranging between .177 and 4.76 mm. in size. rThisslurry is pumped at a rate of 1,000 pounds per hour into a 1K2 inch I.D. tube 17 which is 200 feet long and thence into tube 18. Tube 17 isheated to a temperature of about 220 C., and a pressure of about 95pounds per square inch gauge is maintained at outlet 23. Meanwhile,gaseous hydrogen is pumped into the tube 18, which is 400 feet long, ata rate of 2,500 cubic feet per hour to react exothennically with the hotne particles of copper oxide and produce an extremely finely-dividedcopper powder product. Since the reaction is quite exothermic it isimportant to control the temperature in the tube 18, as by sprayingwater vover the tube from the sprayer 24 to prevent damage to theapparatus.

ln the embodiment of the invention illustrated in Fig. 2, the metaloxide is introduced linto the system and initia-lly ground in the samemanner as described in connection with Fig. 1. However, before thereduction takes place the nely ground metal oxide is separated from thesteam or other vapor, after which the reducing gas picks up andfluidizes the powdered copper oxide to carry out the reducing reaction.

More in detail, the metal oxide and liquid are combined to form a slurryin a mixer 41 and the slurry is then passed in high velocity turbulentow through a preheater 43 and a grinding coil 45 to. 4disintegraterthecopper oxide particles, land then into the separator 47. Vapor passes by'a conduit 49 to the preheater 43. Hot copper oxide passes out through abottom exit 50 and is carried by a reducing gas, such as gaseoushydrogen from a supply conduit 49, into a reactor 51 wherein thereduction takes place. The temperature of the reactants should be atleast 140 C. to initiate the reaction. The initial section of reactor 51can be heated mildly to assure such a temperature. Since the reaction isexothermic the temperatures hould be controlled in the latter part oflthe reactor 51, as by spraying water thereon from a water spray device55.

it is advantageous for the reactor 51 to be a long coiled tube `like thetube 18 of Fig. 1, and for the reduc-ing gas to iiow in such volume andat such a high rate that 1: a violently turbulent ow occurs whichfurther decreases the size of the particles passing through the tub-e.However, when no further size reduction is required, the reactor 51 canbe a simple chamber.

The reduced metal and accompanying gases pass from reactor 51 by aconduit 57 to a separator 59 from which the metal powder produotisdischarged through a bottom exit 61, and the gases are discharged at`the top through a conduit 63. Y Y

The heat of the oli-gases in conduit 63A may be utilized by passing themthrough a hydrogen pre-heater e5.

l tegration to an extremely fine state such that the average diameter ofparticles is of the order of 1 5 microns. There also may be someparticle size reduction due to the rapid expansion and contractioneiects on the particles and the violent transfer of energy to theparticles within the heating zone when liquid is vaporized from theparticles.

l-iy novel method is particularly advantageous because it will producethe finest metal powder continuously, ra idly, and economically withoutrequiring an independent grinding step. It is also of particular valuebecause water vapor wil-l not accumulate on the particle ysurface toinhibit the reaction,Y as in static reduction methods.

The use of a slurry from which liquid is vaporized to carry the solidparticles in a uidized condition through the system is another importantadvantage over prior procedures involving the fluidizing of solids. insuch prior procedures the solid particles must be suspended ldirectly inan expensively compressed gas by complicated apparatus, and ahigherrratio of gas to solid is required Vthan in the present invention.

This application is a division of my application Serial No. 309,394filed September 13, 1952.

Obviously many modications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

I claim:

l. A method for producing comminuted metal from an oxide thereof whichcomprises forming a owable mixture of relatively coarse particles ofsaid oxide in a vaporizable liquid; passing said mixture into andthrough an elongated tubular heating zone; heating said mixture duringpassage through said tubular zone to a temperature suf'cient to vaporizesubstantially all of said liquid component to vapor during passagethrough said zone, forming therein a dispersion of solid particles inresulting vapor; passing said dispersion through a succeeding zone ofhigh velocity ow, subjecting the owing stream therein to turbulence anda high velocity in excess of feet per second thereby effectingdisintegration of said coarse particles of oxide; and reducing saiddisintegrated particles of oxide to metal particles much iiner than theoriginal particles of oxide by introducing into said owing dispersion areducing gas, said reducing gas owing through said succeeding zone withsaid dispersion and. reacting with said particles of oxide toformparticles of metal much -ner than the original coarse particles ofoxide, and holding the temperature below the melting point of saidmetal.

2. A method in accordance with claim 1 wherein said vaporizable liquidis water.

3. A method in accordance with claim l wherein said oxide is copperoxide, and said metal is copper.

4. A method for producing a metal from an oxide thereof in accordancewith claim l0, also comprising separating the gas from the metal soreduced; scrubbing said gas to remove therefrom ingredients other thanunreacted reducing gas; and recirculating the reducing gas so recoveredinto Contact With metal oxide in said ilowing dispersion.

5. A method for producing comminuted metal from an oxide thereof whichcomprises forming a slurry of particles of said oxide in a vaporizableliquid; passing said slurry into a heating zone; heating said slurry toa tempcrature suiicient to evaporate substantially all of said liquid tovapor; passing said particles of metal oxide with said vapor through along tube in turbulent ow and a high velocity suflicient to eiectdisintegration of particles of said metal oxide flowing with said vaporwhile intr0- ducing a reducing gas into said tube to react with saidmetal oxide and form particles of metal, and while maintaining thetemperature below the melting point of said metal; and maintaining suchhigh velocity turbulent ow conditions in said tube to effectdisintegration of particles owing with said vapor and produce as aproduct metal powder much finer than the particles of metal oxide insaid slurry.

6. A method in accordance with claim 5 also comprising discharging vaporand metal powder from said tube; and separating said vapor from saidmetal powder.

7. A method in accordance with claim 6 also comprising passing saidseparated vapor in heat exchange relation with said slurry to preheatthe latter before entering said heating zone.

8. A method in accordance with claim 6 also comprising recycling excessreducing gas from said vapor into said tube. Y

9. A method in accordance with claim 5 also comprising the step ofpassing a cooling uid in contact with the outside of said tube, therebyextracting heat from the reactants in said long tube to keep down thetemperature of the reaction.

l0. A method in accordance with claim 5, also cornprising condensing anyof said vaporized liquid in the vapor so discharged, recycling excessreducing gas from said vapor into said tube, and recycling the liquid socondensed to said slurry.

Kalbach et al. Jan. 16, 1951 Rees et al. Feb. 15, 1955

1. A METHOD FOR PRODUCING COMMINUTED METAL FROM ANOXIDE THEREOF WHICHCOMPRISES FORMING A FLOWABLE MIXTURE OF RELATIVELY COARSE PARTICLES OFSAID OXIDE IN A VAPORIZABLE LIQUID; PASSING SAID MIXTURE INTO ANDTHROUGH AN ELONGATED TUBULAR HEATING ZONE; HEATING SAID MIXTURE DURINGPASSAGE THROUGH SAID TUBULAR ZONE TO A TEMPERATURE SUFFICIENT TOVAPORIZE SUBSTANTIALLY ALL OF SAID LIQUID COMPONENT TO VAPOR DURINGPASSAGE THROUGH SAID ZONE, FORMING THEREIN A DISPERSION OF SOLIDPARTICLES IN RESULTING VAPOR; PASSING SAID DISPERSION THROUGH ASUCCEEDING ZONE OF HIGH VELOCITY FLOW, SUBJECTING THE FLOWING STREAMTHEREIN TO TURBULENCE AND A HIGH VELOCITY IN EXCESS OF 100 FEET PERSECOND THEREBY EFFECTING DISINTEGRRATION OF SAID COARSE PARTICLES OFOXIDE; AND REDUCING SAID DISINTEGRATED